Breach detection in solid structures

ABSTRACT

An implantable device includes at least one solid structure having an external surface and a volume beneath the surface. One or more of a first conductor or set of conductors is disposed externally and/or internally on or within the structure and an array of elongate electrically conductive elements are disposed radially outwardly within the volume. A breach is detected when a conductive fluid intrudes into the volume through the surface.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/599,309 (Attorney Docket No. 41680-704.301), filed Jan. 16, 2015, nowU.S. Pat. No. ______, which is a continuation of U.S. patent applicationSer. No. 13/349,327 (Attorney Docket No. 41680-704.201), filed Jan. 12,2012, now U.S. Pat. No. 8,963,708, which claims the benefit of U.S.Provisional Application No. 61/432,461 (Attorney Docket No.41680-704.101), filed Jan. 13, 2011, the full disclosures of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to medical apparatus andmethods. More particularly, the present invention relates to implantabledevices and methods and systems for detecting their dysfunction orimpending dysfunction.

Implantable medical devices, particularly those indicated for long termuse in the human body, are highly regulated and must meet certain safetyrequirements. It is known that when a device is implanted in the body,the materials forming the cover and structural elements of the devicemay degrade and fatigue over time. It is also known that improper orexcessive handling during implantation could stress the structuralintegrity of the device. In devices with movable mechanical parts, thewear and tear of the materials in contact with each other could lead todegradation of the surface, the interior volume, and eventually thestructural stability of the part itself. Such wear can also releasedebris particles which in turn can cause harm in a variety of waysincluding triggering immune reactions which can cause osteolysis andblocking luminal structures which can cause strokes or bowelobstruction. When large enough, the damaged part of the device couldshred healthy cells and tissues from red blood corpuscles to bone.Failure of the structural integrity of the device can cause not onlydysfunction but severe injury. Often the wear of the device can bemoderated or evened by changes in physical activity. Or the impairedpart of the device could be replaced without difficulty before the restof the device is damaged necessitating more extensive revisionprocedures and rehabilitation. Not only would this enhance safety andreduce costs, the life of the product can be prolonged. Therefore, itwould be desirable to detect, to monitor, or to predict such an eventand take measures before any irreparable damage to the device or injuryto the patient ensues.

Prosthetic devices implanted in numerous locations in the body areprevalent in medical practice and are expected to be of even greaterimportance than ever before. With medical advances human longevity hasincreased the population of elderly needing them. Obesity adds furtherwear and tear on the body. In today's data driven generation, people aremore involved in taking care of their own health. The implications aremany. Initial, primary therapeutic procedures are performed at youngerages and revision or replacement procedures are increasingly morecommon. Device statistical lifecycles are no longer satisfactory aspatients need information specific to the device implanted in their ownbody and individualized counseling. Having a device that can be selfmonitored economically by the patient would be further helpful andreduce overall healthcare costs.

Many devices, such as cardiovascular valves, have parts that are dynamicwhen performing their function and cannot be stopped for examination.Thus failure prediction and detection often depend on secondary signs,such as errant flow patterns by imaging such as ultrasound. By the timetheir function is impaired enough to be detected, the wear and tear tothe device has already far progressed to require more urgent treatment.Early detection of partial failure through a direct or primary methodwould enable more accurate diagnosis and better treatment planning.

Other devices suffer repeated or cyclical stresses from deliberatemanipulation or secondary body movement. Devices such as insulin orother drug pumps require refilling of the reservoir, typically through aneedle. Repeated stabbing in the same location could induce andpropagate these defects in the covering that could allow intrusion ofbody fluids and impair the precisely calibrated functions. Or therefilled fluid could leak through the defects established or propagatedby the injecting device. Electronic stimulation devices, such asneurostimulators, and many mechanically restrictive devices, such aslapbands used in bariatric surgery, require fixation of certain criticalcomponents to body tissues. As the device and the body tissues are notisolated from motions of the rest of the body, any movement could causemechanical stress and, over time, fatigue leading to tears ordislocations of the device.

For these reasons, it would be desirable to provide apparatus andmethods to detect, to monitor, or predict an actual or potential breachof a surface, layer, or body of an implantable object or device in thebody. Prompt removal and/or replacement of such impaired devices orcomponents thereof could avert many, if not all, of the problemsassociated with failure of such devices. The methods and apparatus wouldpreferably be adaptable for use in many devices without adverselyaffecting the device's performance or structural integrity. It would bebeneficial if the device could be directly examined while functionallydeployed in motion without interfering with its performance, eventemporarily. It would be further desirable if the breach of the devicewere detectable to the patient in an easy, rapid, and reliable fashionat home and in other settings away from the doctor and hospital.Additionally, it would be beneficial if the system were able to monitorthe device non-invasively on a frequent basis without incurringsignificant additional cost for each diagnostic event. At least some ofthese objectives will be met by the inventions described hereinafter.

2. Description of the Background Art

U.S. 2006/0111777 and U.S. 2006/0111632 describe inflatable and rigidimplants having embedded conductors utilizing transponders to signal abreach. U.S. Pat. No. 5,833,603 describes an implantable transponderthat can be used to detect breach or wear in implantable devices. Breastimplants and methods for their use are described in U.S. Pat. Nos.6,755,861; 5,383,929; 4,790,848; 4,773,909; 4,651,717; 4,472,226; and3,934,274; and in U.S. Publ. Appln. 2003/163197. Gastric balloons andmethods for their use in treating obesity are described in U.S. Pat.Nos. 6,746,460; 6,736,793; 6,733,512; 6,656,194; 6,579,301; 6,454,785;5,993,473; 5,259,399; 5,234,454; 5,084,061; 4,908,011; 4,899,747;4,739,758; 4,723,893; 4,694,827; 4,648,383; 4,607,618; 4,501,264;4,485,805; 4,416,267; 4,246,893; 4,133,315; 3,055,371; and 3,046,988 andin the following publications: US 2004/0186503; US 2004/0186502; US2004/0106899; US 2004/0059289; US 2003/0171768; US 2002/0055757; WO03/095015; WO88/00027; WO87/00034; WO83/02888; EP 0103481; EP0246999;GB2090747; and GB2139902.

BRIEF SUMMARY OF THE INVENTION

The present invention provides devices, systems and methods fordetecting partial or complete breach of a surface or volume of solid orother non-inflatable structures or components of an implantable deviceto predict device dysfunction or failure of the structure, component, ordevice as a whole. The solid or other non-inflatable structures of thedevice can be made of any solid material including but not limited topolymers, metals, minerals, ceramics, biologics, and their hybrids.Common examples include articular components of prosthetic joints wherethe entire volume is solid. Other structures in implantable devicessubject to such breach include hermetically sealed rigid-walledenclosures, such as those of implantable defibrillators orneurostimulators, or reservoirs, such as those in implanted insulin ordrug pumps, where the volume includes other parts of the device whethergas, liquid, or solid.

Typically the solid structures are subject to breach in areas wherethere is extensive contact between the device and body tissues or withan external object or between different parts of the device. If thedevice is manipulated periodically, the area of wear and tear is at thesite of stress and fatigue of the manipulation. While the implementationof these systems and methods will be described in detail in connectionwith orthopedic joints, it will be appreciated that the principles maybe applied to other non-inflatable prostheses. The systems of thepresent invention are incorporated into at least a portion of thesurface, layer, or thickness of the non-inflated prosthesis and providefor the emission or transmission of a detectable electronic signal uponbreach or partial breach of the same. As used hereinafter, the term“breach” will refer to any partial or full penetration of a surface,layer, or thickness of a structure, or other mechanical disruption whichcould initiate or lead to the contact of heretofore unexposed devicematerials with surrounding tissues or body fluids.

The signal emission system of the present invention preferably comprisesa signaling circuit having one or more components which become exposedto an exterior or interior environment surrounding or within theprosthesis upon breach or partial breach of the surface, layer, orthickness, wherein such exposure enables, disables, energizes,discharges, and/or changes a signal which is emitted by the system. Inparticular, the breach will typically close an open region within thesignaling circuit to cause, enable, disable, or alter the signalemission.

In a first embodiment, the component of the signaling circuit willgenerate electrical current when exposed to a body fluid by the breach.In such cases, the generated electrical current can power an unpoweredtransmission component to emit the signal. Alternatively, the power canalter a signal which has already been continuously or periodicallyemitted by the signaling circuit. In the latter case, the signalingcircuit may require a separate source of energy, such as a battery orcircuit components which can be placed on either side of the surface,layer, or thickness so that they are always exposed to fluids to providefor current generation. Devices near parts of the body engaged inmovement may utilize piezoelectricity to power the circuit. Optionally,the current can throw a switch irreversibly, i.e., entered into memory,so that its altered state can be detected at a later time.

Alternatively, the circuit components may include spaced-apartconductors which are electrically coupled to the signaling circuit to“close” the signaling circuit to permit current flow when exposed to abody fluid in a breach. In the exemplary embodiments described below,the detection portion of a conductor acting as a probe comprise elongateelements embedded beneath the surface, layer, or thickness of thestructure in the location subject to breach with an axis oriented towardthe direction of the breach. As used hereinafter, the embedded“conductor” or “probe” refers to the detecting element including, ifpresent, a cover that electrically insulates it from surrounding tissuesor body fluids. In this unexposed and electrically isolated position,the probe conducts no current and is electrically inactive. A breachthrough the surface, layer, or thickness will expose and electricallyactivate the otherwise isolated probe and provide a channel for theintruding electrically conductive bodily fluids bridging the probe andother conductors. The coupling of the spaced-apart conductors may alsocause, alter, or enable a signal emission to alert the patient of thebreach or potential breach. The probes can have any one of a variety ofshapes or a combination of them to fit the geometry of the structure orthe contour of its surface, layer, or thickness and match the geometryof the breach. A single conductor can expand at the distal end, branchout into a multi-pronged configuration, or run in a continuous loopconfiguration in order to cover a wide area subject to breach tominimize potential disruption to the integrity of the structure.Alternatively, when disposed in a material that is resistant todelamination, the conductor can be shaped in a planar configuration,such as a mesh or a continuous plate, to expand the coverage area ofdetection. Alternatively, the conductor could be made of a material,such as a polymer or metal, in a three dimensional framework thatsupports the integrity or stability of the structure. The shallowestsections of the embedded probes can be situated in various locations,preferably near portions of the structure where the most wear and tearis anticipated to enhance sensitivity and reliability of the detection.Conductors separately coupled to the logic circuit can be embedded atdifferent distances from a surface, layer or thickness to detect notonly the breach but the extent of it through the volume. They can beseparately embedded in different components or sections of them todistinguish the location of the breach. The breadth of the coveragearea, the density of probes, and/or the alignment of the probes could becorrelated to the seriousness of the breach to minimize the potentialthat such a breach is missed.

In a preferred embodiment, the signaling circuit will comprise a passivetransponder and antenna which are adapted to be powered and interrogatedby an external reader. Such transponder circuitry may conveniently beprovided by using common radiofrequency identification (RFID) circuitrywhere the transponder and tuned antenna are disposed on or within theprosthesis and connected to remaining portions of the signaling circuit.For example, by connecting the transponder circuitry to “open”conductors which may be closed in the presence of body fluids, thesignal transmitted by the transponder upon interrogation by an externalreader may be altered. Thus, the patient or medical professional mayinterrogate the prosthesis and determine whether or not the prosthesisremains intact or a potential breach exists. This is a particularlypreferred approach since it allows the user to determine that thetransponder circuitry is functional even when a breach has not occurred.In passive circuits where the antenna derive power from incomingradiofrequency signals, the antenna is preferably fixated in aradiofrequency privileged location relatively in parallel to the surfaceof the overlying tissues and/or skin. In this fashion, the plane of theantenna can be orthogonal to the radiofrequency vector in order tomaximize radiofrequency induction and signal strength. If there isradiofrequency interference from materials nearby, the antenna and/orthe circuit will have shielding in the substrate or encased to minimizethis effect. To minimize interference even further, the circuitry may beseparated from the antenna with the sensitive portions fixated toprivileged sites on the device or to the surrounding tissue.

The present invention further provides methods for signaling breach of asurface, layer, or thickness of a structure in a prosthesis. Usually, awireless signal emission comprises closing a circuit when the surface,layer, or thickness is at least partially breached or generating anelectrical current when the surface, layer, or thickness is at leastpartially breached. The particular signaling circuits and transmissionmodes have been described above in connection with the methods of thepresent invention.

The signaling system of the present invention can be designed tofunction in a variety of algorithms to notify the patient in a simple,unequivocal fashion. For example, in a toggle algorithm, the transmitteris either on in the static state or preferably off in order to reducethe need for power. Upon direct contact with the body fluids and ordevice contents, the conductors cause the transmitter to turn the signaloff or preferably on to be able to send a wireless signal on acontinuous basis. The wireless signal or lack thereof is recognized bythe detector to notify the patient that the integrity of the device iscompromised. Optionally, the conductors can cause a switch to be thrownirreversibly so that its altered state in the memory can be detected ata later time. Optionally, the conductors can cause a switch to be thrownso that other functions of the device are enabled.

Alternatively, the algorithm could be based on time, amplitude,frequency, or some other parameter. For example, the transmitter may beenabled to emit a wireless signal at a predetermined time interval inits static state. The detector recognizes the length of the interval asnormal and the existence of the signal as the system in working order.Upon direct contact with the body secretions or device contents by theconductors, the transmitter is enabled to send the same signal atdifferent time intervals or a different signal, which is recognized bythe detector to notify the patient that the integrity of the device iscompromised. The lack of a signal is recognized by the detector tonotify the patient of a detection system malfunction and potentialcompromise of the integrity of the device.

Optionally, more than one probe or more than one type of probe may beplaced internally in different parts or components in the device so thatthe particular part or component which failed may be identified based onwhich probe was activated. The transmitter would send different signalsfor the receiver to display the source of the failure. Optionally, theycan be separately embedded in different locations of the same part.Diagnostics amongst the various parts or sections can be easilydifferentiated with the RFID codes assigned to each part or section.Optionally, probes could be coupled to detect, identify, and/or monitorthe cause of the breach, especially in the situation where the materialof the structure is subject to a breach by certain chemical orbiological agents which may or may not normally be present in theenvironment. Optionally, two or more probes could be coupled to detector monitor the extent of the breach in another parameter value. Forexample, wear and tear often result in the shedding of small debrisparticles. The detectable presence of these particles, particularly ifthey have intrinsic or contain ingredients that have electromagneticproperties, and the concentration of them in the surrounding body fluidscould be monitored by the coupled probes thereby giving an indication ofthe site of the debris and the volume of the wear. Optionally, probesactivated by the breach could serve as a composite for imaging thelocation, extent, and depth of the breach. The data from the probes canbe plotted on a map to visualize the projections.

The probe is a three dimensional conductor disposed in the materialdirectly underneath the surface, layer, or thickness subject to breach.Embedded in this position, the conductor is directly behind the surface,layer, or thickness in the advancing path of the breach into thestructure. Exposing the conductor, therefore, is ipso facto evidence ofthe breach penetrating through the surface, layer, or thicknessoverlying the conductor. Depending on the configuration, the conductorcan be situated to detect breaches in multiple sides of the structureand from multiple directions. The most sensitive embodiment is planar,such as a fine mesh, lattice, or continuous film of the detectionmaterial embedded in the material or in between layers of the materialsof the structure. In general, such a configuration optimizes theperformance of the system in detecting failures early. If the site ofthe tear or rupture cannot be predicted, the probe would be unlikely tomiss detecting the breach by covering the entire device, as discussed incommonly owned prior patent publications US 2006/0111777 and US2006/011632, the full disclosures of which are incorporated herein byreference.

A continuous film, mesh, or lattice may be preferred for inflatable orfillable devices where the site of breach is unpredictable and completefailure can result from a very small breach. However, for somenon-inflated structures or devices, a continuous film, mesh, or latticemay not be required or even ideal. Most non-inflatable devices do notfail from pinpoint breaches but later from the propagation of them. Inorthopedic prostheses, the areas of stress and fatigue are often wellidentified and circumscribed. For example, in prosthetic orthopedicjoints certain structures and parts of them suffer the brunt of thevarious forces from load bearing. These include but are not limited tocompression, dispersion, shear, rotation, friction, and combinations ofany of them. Motility usually involves repetitive and cyclical movementsof certain body parts. Consequently, particular areas on the articularsurfaces suffer the most from these forces and are the most susceptibleto degrade and eventually break down from wear and tear. Moreover, thewear and tear is not uniform, layer by layer, because articular surfacesdo not experience fixed directional forces applied evenly. This isexacerbated with dedicated sports activities although the particularareas affected are specific for the sport. For others, such ascardiovascular valves, the leaflet edges encounter the most stress fromcycles of opening and closing. For devices fixated to body tissues,repetitive and cyclical forces from normal body movements exert strainon particular areas on certain structures. The breaches on thesefixation structures, such as locking mechanisms and anchors, again canstart at an edge or corner and propagate inward or across the structure.Such mechanisms do not have to have sudden failure to cause a meaningfuleffect. Mere loosening of a functional part, such as in a lap band,could be the difference between therapeutic success and failure.

A continuous film or lattice could even be disadvantageous fornon-inflatable and non-fillable devices. For many, such an embodimentembedded as a layer may actually weaken the structure subject to breach.Corrosion of the device can start in several ways. It could begin as asmall crack or tear into the surface or deep in the layer of a loadbearing area from a compressive force. Or the surface could begin to pitfrom friction and shear due to repetitive lateral and rotationalmovements. Thereafter, shards or small layers of the material areabraded off the protruding edges. As the breach progresses into thevolume, the exposed materials continue to erode and wide pits result. Ifthe structure has convexities, they can shear and flatten. This is acontinuing material science problem in the design of orthopedic implantsfor product longevity. Metal and plastic parts are typically titanium orcobalt-chromium alloys and ultra high molecular weight polyethylene,respectively, to balance the needs for strength, flexibility, lubricity,and shape retention. In some instances, synthetic ceramics are also usedfor their special properties. Surface hardening processes from sinteringto special coatings are common. Incorporating the conductors, and ifneeded, its insulation, as additional planes or layers into differentmaterials introduces surface-to-surface adhesion and differential shearresistance among other problems that could increase susceptibility topropagation of wear and tear and sudden failure. If there is anychemical or biological corrosion, it could travel along the naturalplane in the interface between different materials. Therefore, such aplanar configuration could even result in accelerated degradation,especially through deformation or delamination.

Given the lower sensitivities required and the non-uniform wear and tearcharacteristics in certain non-inflatable structures, a probeconfiguration with minimal potential to change the performance ordurability of the structure is desirable. In the preferred embodiment,it is a three dimensional array or arrangement of one or more elongateelements embedded beneath the surface, layer, or thickness subject tobreach as described in greater detail below and the accompanyingfigures. The detecting portions of the probe project from deeper levelsin the volume and end at predetermined distances from the surface, layeror thickness. From the surface, an array of points and/or broken linesor curves at predetermined depths is presented to detect the breach.Such an embodiment is minimally disruptive to the overall integrity ofthe structure while allowing configurations that can maintain coverageof the detection to a wider area.

The probe material could be made of any biocompatible metal, polymer,gel, fiber, particle, ingredient, or combination thereof, with orwithout any coating or particle impregnation that can generate anelectrical charge or enable flow of electric current when in contactwith the body fluids or device contents. For example, an electricalcharge could be generated from a non-toxic chemical reaction when theelongate element exposed underneath a tear comes in contact with thebody secretions. Flow of electric current could be enabled when two endsof an electric circuit hitherto physically separated by electricallynon-conductive material in the covering or a structural element of thedevice are in contact with electrolytes in the body secretions when theintervening electrically non-conductive material is compromised. Forexample, a charged elongate element is embedded in the core materialseparate from the ground probe on the external surface of the device.When the elongate element is exposed to the electrolytes in the bodyfluids in the event of a tear, the circuit is closed. Alternatively, thecharged and ground probes could be physically adjacent but electricallyseparate from each other in the material of the structure and bothexposed to body fluids by a breach. Preferred materials includenon-corrosive, biocompatible metals and elastomers, inks, or the likewhich contain electrically conductive particles. They can be rigid ornon-rigid. To minimize effects on the material properties andperformance characteristics of the structure, it is preferably in thesame class of materials or has compatible physical and/or chemicalproperties as the surrounding materials in the structure subject tobreach. So long as the materials of which the elongate element is madeare in electrical contact, they can be in any physical composition, evenincluding but not limited to loosely compacted particles or suspensionssuch as gels. In these alternatives, they can readily assume an alteredshape if the structure can deform prior to a breach. If the conductormaterial is more durable than the material surrounding it, the conductorcould even be designed by one skilled in the art to serve an extrafunction as reinforcement for the structure itself.

Optionally, a conductor material is selected for its intrinsicbiochemical effect. For example, silver and gold have naturalanti-infectious and anti-inflammatory properties, respectively. Embeddedin the structure, the conductor materials are released in dosesdepending on the magnitude of the breach. Optionally, the probes can bedesigned by one skilled in the art to function as carriers forbiochemical agents, which are eluted and/or activated when exposed bythe wear and tear. For example, antibiotics could be delivered to fightinfectious organisms or anti-inflammatory agents, such ascorticosteroids, to moderate inflammatory responses. Should these agentsbe electrically non-conductive, they could be incorporated in theinsulating cover for the elongate element. Shielded by the intactstructure, these agents would lie in waiting for the moment thestructure is breached. Given that the release in a breach is immediateand localized, very small amounts of the agents could be effective incontrolling these complications early in the process, often far beforethey become symptomatic. Worn off with the debris of the structureitself, these agents travel with the debris like chaperones. Instead ofselecting the materials for their therapeutic value, the materials maybe selected for their properties for diagnostic value. For example, thematerials could facilitate diagnosis and monitoring for their radio orsono contrast, luminescence, or other chemical or physical properties.Once a breach has been detected, the extent of the distribution and theload of the debris can be imaged non-invasively by readily availableradiographic or sonographic equipment. Again, should these agents beelectrically non-conductive, they could be incorporated in theinsulating cover for the elongate element.

The conductive elongate element in the assembly can be in variousconfigurations to suit the detection criteria and match the contour ofthe surface, layer, or thickness subject to breach and the geometry ofthe breach. In its most basic form, the elongate element is a simplecylinder of conductive material. Optionally, it is tapered at the distalend to be minimally disruptive to the structure nearer the surface,layer, or thickness subject to breach. If the material of the structurein which it is embedded is electrically conductive, the elongate elementis insulated such that the entire element is of a cylinder or cone inshape. In this configuration, the probe presents a conductive point atthe desired depth to detect the breach. This may be sufficientlysensitive if the breach is expected to assume the shape of a shallow andwide depression from shearing and abrasion. Optionally, the conductor isa loop or coil to widen the coverage area or to detect widening breachtrajectories. In this configuration, detection of a linear split isenhanced since such a breach could easily miss a point but is likely toextend across and expose a portion of the loop. The coil can be uniformin diameter of a cylinder or has the overall geometry to match theexpected path of the breach. For example, an inverted cone might bepreferred in a breach that has a small entry but propagates widely deepbeneath a surface, layer, or thickness, especially one that has beenprocessed to increase durability. Optionally, the loop can spread out inan expanded pattern within a thickness constituting a patternedconductive line to detect an incoming breach. Optionally, a conductorcomprises branches of individual elongate elements arrayed or arrangedin a multipronged formation presenting an array of points to detect thebreach and the main branches much further behind to minimize thepotential disruption to the physical integrity of the structure. Theseprongs can approach the surface, layer, or thickness at any angle, be ina staggered formation, and/or crisscross each other. Whether thesurface, layer, or thickness is flat, convex, or concave, the aboveconfigurations or a combination of them could be embedded at suitabledepths and densities to detect the existence and extent of the breach.In these configurations, the points or discontinuous lines that end ateach uniform distance from the surface, layer, or thickness constitute aline or plane that is parallel to the surface, layer, or thickness.

For surfaces, layers, or thicknesses with complex contours orsilhouettes with mixed flats, protuberances, and indentations, it may beproblematic to embed precisely the elongate element conductors atuniform depths and/or densities amongst the peaks and valleys ofstructure or to incorporate multiple conductors without threatening theintegrity of the structure. In this situation, the conductive elongateelement could be configured as a continuous loop following such contoursor silhouettes such that conductive points or broken lines are presentedat a uniform distance from such surface, layer, or thickness to detectthe breach. Certain portions of the elongate conductor can project outand others depress in to vary the placement of the conductive linewithin a thickness. The shallowest or detecting sections of the embeddedprobes can be situated in various locations, preferably near portions ofthe structure where the most wear and tear is anticipated to enhancesensitivity and reliability of the detection. Such a configurationenables monitoring a large, prescribed area or a specific structuralfeature with a single conductor. Optionally, the continuous loopfollowing such contours or silhouettes can present conductive points ordiscontinuous lines or curves at different distances from such surface,layer, or thickness to match the relative probabilities or importance ofbreaches at different locations.

Regardless of the geometry of the three dimensional formation of theassembled elongate elements, at least one major axis of theconfiguration is aimed toward the direction of the breach. Usually, thisis the axis in alignment with the detection portion of the probeprojecting toward the direction of the breach. Typically for a flatsurface, layer, or thickness, the axis is the longitudinal which isoriented orthogonal to the surface, layer, or thickness. For a simpleconvex or concave surface, layer, or thickness this axis isperpendicular or at an angle to the tangential plane depending on thetolerances in manufacturing, impact on the structural integrity, and/ordifferences in performance characteristics. Where the contour of thesurface, layer, or thickness is complex requiring a continuous loop orcoil, the preferred axis is the radial intersecting the tangentialplane. In this instance, the shallower portions of the conductor projectto and are oriented to the contour. Alternatively, if the trajectory ofthe breach branches out, for example in a cylindrical structure, theradial axis may be directed inward any branch in propagation.

The conductive probes, with or without insulation, can be incorporatedinto the non-inflatable devices in a variety of manufacturing processeswell known to those skilled in the arts. For example, for types oftechnologies such as casting or molding, the preformed conductor can beplaced in the mold at the exact distance from the surface, layer, orthickness and precision casted or molded together with the surroundingcore materials to form the structure. Or a bore for the probe can becasted, for example, using the lost wax method. For material removal andforming types of technologies, the component can be precision machinedby a computer numerical controlled tool, preferably from behind thesurface, layer, or thickness, to form bores or shaped spaces forfixating the conductor. In this direction of machining the component,the surface, layer, or thickness to be monitored would be preserved as apristine, continuous barrier for the breach. In addition, sources ofabrasion or breach, such as any physical deformities or imperfectionsleft behind by machining from the front and any sealing or fixationmethod, would be obviated. For accretion manufacturing technologies, theconductor can be built into the original substrate or the built part canbe machined as above. In the former, for example, the conductor and/orits fixation is held in place as a node and the material of thestructure is injected onto and around it from different directions orlayer by layer to build up the desired three dimensional structure. Ifthe material is a biologic, the surface of the conductor with itsinsulation could be engineered to have adhesive properties for theaggregation of the cellular components and growth of the tissue. In thelatter, as in the other manufacturing processes, once the bore for theconductor is formed, the conductor can be placed and fixated onto thestructure by a variety of processes depending on the material. If it isa solid, the conductor can be inserted directly into the bore andfixated. Alternatively, the bore can be filled with a conductive fluidor paste and then, if needed, transformed into a solid by a variety ofmeans known to those skilled in the art, for example, heat orultraviolet light curing. The conductor can be uninsulated if thematerial of the structure is electrically non-conductive. If thematerial of the structure is conductive, insulation can be preformedover the conductor or placed in the bore prior to introducing theconductor. However, whether the structure material is conductive or not,the conductor is preferably surrounded by insulation along its length tothe circuit to form a continuously insulated and electrically isolatedappendage prior to placement. In this fashion, there would be no seamthat could be poorly sealed or opened after deployment for body fluidsto intrude and cause the circuit to send a false positive signal of abreach of the structure. Because of the various axes along which theelongate elements of the conductor are embedded in the structure andpotentially tortuous bore, precise machining may be challenging. In thissituation, the component can be constructed in three steps. A housing,such as a shaped plug, containing the conductor is first constructed asa male member by any of the processes described above. The component isthen precision machined as the female member, preferably from behind thesurface, layer, or thickness to hollow out the correspondingly shapedcavity to receive the plug. The plug can be inserted and fixated througha variety of means, including but not limited to mechanical, chemical,physical, or hybrid technologies known to those skilled in the art.

Typically, the component will need to undergo finishing processes. Theyrange from mechanical processes such as polishing to removeimperfections to chemical processes such as coating and sintering toharden the surface. So long as the process does not involve hostileconditions for the conductor assembly and circuitry, the component canbe finished with installed conductor. In most situations, however, itwill be preferable to complete the surface finishing process beforeinstalling the conductor. The treated surfaces can simply be protectedduring the component assembly. The entire circuitry could be furtherattached, encased, or hermetically sealed to the assembled component inprotective material to form one solid piece, if needed.

The transmitter in the circuit can be a simple wireless signal generatortriggered by an electric current or preferably a transponder using thewell-established RFID technology, i.e., produces a wireless signal whentriggered by an interrogating signal. The electric charge generated orthe electric current enabled by the probe in contact with the bodyfluids or device contents enables the transmitter to emit or causes itto emit a wireless signal. Typically, the transponder is powered by theinterrogating radiofrequency signal so that no power source of its ownis required. Alternatively, the transmitter could be powered internallyby a micro battery or externally by induction. Alternatively, power canbe generated by a chemical reaction or piezoelectricity from surroundingbody tissues. The circuitry is placed on a substrate which may includeshielding to protect it from electromagnetic interference. Forprotection from degradation by an acidic and electrolyte solution andbecome potentially toxic, the transmitter or transponder circuit isencased in a highly resistant material, such as silicone rubber, glass,polycarbonate, or stainless steel. The transmitter or transpondercircuit can be placed in the interior or on the exterior, preferablyaway from an area of mechanical stress and electromagnetic interference.The antenna can be placed in a separate radiofrequency privilegedlocation from the circuit but is preferably in an orientation that ismost sensitive in sending and receiving signals through body tissueoverlying the device. The circuitry and any of its parts may bemechanically fixated to preferred sites on the device or to the tissuein a variety of means known to those skilled in the art. Many of theabove teachings are exemplified in the embodiments of the invention inthe detailed descriptions of the inventions below.

The wireless signal from the transmitter is recognized by a detectorexternal to the body. The detector could be simply a receiver tuned tothe transmitter's signal or, preferably, a combination of both atransmitter of a signal to interrogate the transponder and a receiver todistinguish the different signals from the transponder. The detector ispreferably powered by batteries and portable enough to be handheld, wornon a band or belt, or can be placed conveniently near a place where thepatient visits often or spends most of his time. Upon receiving a signalthat a breach has occurred, the detector will alert the patient to seekmedical assistance or alert medical professionals directly through otherdevices, such as Bluetooth linked to an autodial telephone. The alarmcould be auditory, such as beeping sounds, visual, such as flashingLED's or a LCD display, sensory, such as vibrations, or preferably acombination of any or all of the above.

Optionally, the detector could have different auditory, visual, sensory,or different combinations to identify the source of the detected breach,especially with more than one probe or more than one type of probe. Forexample, LED's of different colors or different sounds could be used.The alarm could further indicate the seriousness of the breach. Forexample, when multiple probes detect a breach, the volume of the alarmwould increase to a higher level. Upon receiving a signal indicating adysfunction or impending dysfunction of the device, the patient wouldseek prompt medical care for the timely replacement of the impaired partor component before serious complications. Optionally, the signalsindicating the breach from the probes could be compiled into an image toshow the location, extent, and depth of the breach.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-C illustrate the radiofrequency circuitry in threeconfigurations of the breach detection system of the present invention.

FIGS. 2A-2E illustrate the various configurations of the detectingportion of the second conductor as an elongate element.

FIG. 3 illustrates the orientation of the detecting portion of thesecond conductor as an elongate element to the direction of the breach.

FIG. 4 illustrates an alternative configuration of the elongate elementand an example of the method of embedding the elongate element in thematerial behind the surface, layer, or thickness in the direction of thebreach.

FIGS. 5A-5D illustrate additional configurations of the elongate elementwhere the detection portion of the second conductor is spread out in anexpanded pattern to cover a wider area and increase the sensitivity.

FIGS. 6A-6D illustrate further configurations of the second conductorwhere two or more elongate elements are combined and coupled in amultipronged formation aiming toward the direction of the breach.

FIGS. 7A-7B illustrate location and orientation of the elongate elementsof the second conductor incorporated in a structure with a convexsurface, layer, or thickness over a volume.

FIGS. 8 and 9 illustrate location and orientation of the elongateelements of the second conductor incorporated in a structure with aconcave surface, layer, or thickness.

FIGS. 10A-10C illustrate another configuration where the elongate is along spiral, coil, or helix.

FIGS. 11A-11D illustrate how a loop or coil configuration of theelongate element is incorporated in more complex surfaces, layers, orthicknesses.

FIGS. 12A-12C illustrate a knee prosthesis having the breach detectionsystem of the present invention incorporated in the components on thetibial side.

FIGS. 13A-13B illustrate a knee prosthesis having the breach detectionsystem of the present invention incorporated in the femoral component.

FIGS. 14A-14C illustrate the various wear and tear forces that the kneeexperiences during stances and movements leading to a breach of asurface, layer, or thickness.

FIGS. 15A-15B illustrate the operation of the passive transponderdetection system in the knee prosthesis with a handheld reader.

FIGS. 16A-16B illustrate the various wear and tear forces that the hipexperiences during stances and movements leading to a breach of asurface, layer, or thickness and a hip prosthesis having the breachdetection system of the present invention incorporated herein.

FIGS. 17A-17B illustrate a hip prosthesis having the breach detectionsystem of the present invention incorporated in the femoral headcomponent.

FIGS. 18A-18D illustrate a hip prosthesis having the breach detectionsystem of the present invention incorporated in the acetabular cupcomponent.

FIG. 19 illustrates the operation of the passive transponder detectionsystem in the hip prosthesis with a handheld reader.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIGS. 1A-1C, the radiofrequency circuitry of the deviceis shown in three configurations, each with four major parts, a firstconductor 110, a second conductor 120 (a distal end for detection shownin figures below in more detail), a logic circuit 130, and an antenna140. The logic circuit 130, unless split into distinct parts, for thedescriptive purposes here includes the transmitter and transponder.Conductors 110 and 120 are electrically isolated from each other until abreach exposing the conductor 120 to an electrically conductive fluidintruding into said breach bridges them. In circuitry 151, the logiccircuit 130 is on the same substrate as the antenna 140. In circuitry152, the logic circuit 130 is fixed on another substrate apart from theantenna 140 to accommodate design requirements for size and location,esp. to enhance sensitivity, specificity, or robustness. In circuitry153, the logic circuitry 130 and a ferrite core antenna 140 is fixedinside a hermetically sealed capsule. It will be obvious to an ordinaryperson skilled in the art that the circuit could be split further inparts on separate substrates to satisfy design requirements. In passivecircuits where the antenna derive power from incoming radiofrequencysignals, the antenna is fixated relatively in parallel to the surface ofthe overlying skin. In this fashion, the plane of the antenna can beorthogonal to the radiofrequency vector in order to maximize capture ofradiofrequency energy. The radiofrequency reception can be also beenhanced, such as shown with a ferrite core antenna. Conductor 110 isshown as a single lead wire but can be in any form or shape (not shownhere), including the variety of configurations as the conductor 120below, or electrically coupled to other conducting materials so long asit is electrically exposed to an electrically conductive fluid when thedevice is implanted in a body or in the event of a breach. Conductors110 and 120 are shown here in their proximal link to the logic circuit130 and the double hashed lines indicate the linkage to the distaldetecting portion of the conductors.

FIGS. 2A-2E show the distal detecting portion of the second conductor asan elongate element in various configurations. In these and all of thefollowing configurations, should any material be incorporated forenhancement, such as pharmacologic therapeutic or diagnostic agents,whether in the conductor or its insulation, it is not shown separatelybut represented within the whole. The second conductor 221 is a simplecylinder containing a core of conductive material 202 or a combinationof such materials 202. The conductor can be a bare wire if the devicematerial surrounding it has sufficient impedance to electricalconduction. The overall shape of the second conductor 205 including theconducting material 202 and the optional insulating or fixating material207 surrounding it can be in any elongate form, here shown as a cylinderin conductor 222 or a cone in conductor 223. Conductor 203 is shown in atapered configuration. In conductor 224, the first conductor 201 isadjacent to the second conductor 202 with insulating material in themiddle separating them. At their distal portions, the conductors can beside-by-side, wrapped around each other, loop one around the other, oneconcentric to the other or form a double helix formation. These closeproximity configurations of the first and second conductors 204 isparticularly advantageous in specific situations where the firstconductor must also be unexposed electrically or, for example, detectinga breach that would expose both conductors simultaneously is desired. Ifnot shown in later figures, this configuration of both the first andsecond conductors located next to each other may be assumed by figuresof only the second conductor. In conductor 225, the shape at the tipforming the frontline of the detection may be enlarged or enhanced witha plate, lattice, film of conductive material. In this figure and insubsequent figures, the double hashed lines indicate the linkage to thelogic circuit 130 in FIG. 1.

FIG. 3 shows the detection portion of the second conductor as anelongate element with a longitudinal axis oriented toward the directionof a breach. As described in FIG. 2 above, the overall shape may be inany elongate form, here depicted as a cone. The surface, layer, orthickness to be breached is depicted as full or total in 362 or aspartial in two layers 361 and 363. Each surface, layer, or thicknesswhile depicted as separate may themselves be made of thicknesses ofdifferent materials or is made of the same material as the core 364.Thicknesses 361 and 363 could even represent the processed surface of astructure made from a uniform material through a variety of technologiesby one skilled in the art to increase durability. The conductors 321,322, and 323 are embedded in the core material 364 beneath the exposedoutermost surface 360 extending toward and into the surface, layer, orthickness for a fixed distance. The direction and path of the breach isshown as 370 and the conductors are disposed at the interface or planebetween the surface, layer, or thickness subject to breach and the layeror thickness of the material underneath it. In this location, theconductors are directly behind the layer or thickness and in front ofthe core material in the path of the breach. In conductor 321, thedetection tip 325 closest to the outermost surface extend through layer363 and end at the partial thickness 361 to detect a partial breach andin conductor 322, at the full thickness to detect a complete breach. Itwill be appreciated that the depths of the breach can thus be detectedby a number of embedded conductors with tips ending at predeterminedlevels. The conductor is oriented toward the direction of theanticipated breach with the longitudinal axis perpendicular inconductors 321 and 322 and slanted at an acute angle in conductor 323.Regardless of the angle of approach, it is readily seen that thelongitudinal axis of the elongate element intersects the plane of thesurface, layer, or thickness subject to breach. Note that the surface362 may be exposed to an interior and direction of the breach may befrom an interior toward an exterior but the conductors are oriented tointercept the breach.

FIG. 3 also illustrates how the elongate elements 321, 322, and 323intersect a planar region of the implant at different angles, typicallybetween 60° (323) and 90° (321).

Referring now to FIG. 4, an alternative serpentine configuration of theelongate element is shown. The top views are not shown but comprise asimple round coil spiraling from the depth toward the surface. The tailof the conductor may also traverse laterally to connect with thecircuitry (not shown). Each is embedded in the material terminatingdirectly behind the surface, layer, or thickness in the direction of thebreach path 370. The detection section can reside in one or more layersof thicknesses at different depths. In this configuration, the elongateelement is wound or looped in a spiral or coil with its distal,detecting portion projected toward the anticipated breach. Conductor 421is coiled into an overall shape of a cylinder; 422, an inverted cone;and 423, a cone. In these three conductors, the sensitivity is increasedby enlarging the area of the detection zone or detecting breaches thatbranch and propagate laterally. In conductor 422, the inverted conecould be useful in detecting a breach that has a small entry in ageneral area through a surface, layer, or thickness but propagates morewidely under it. Conductor 423, having a cone shaped spiral, wouldpresent less disruption at the surface, layer, or thickness it ismonitoring and yet have width of coverage proportional to the depth ofthe breach. Conductor 424 is configured as a double helix with the firstconductor 410 and second conductor 420 looped in close proximity to eachother with insulating material in between them. This wound togetherconfiguration is particularly advantageous if the first conductor mustalso be unexposed electrically or detecting a breach that would exposeboth conductors at the same time is desired. For ease and flexibility inprecision manufacturing and assembly, the elongate element is embeddedin exemplar fashion into the material, here shown as a conductor encasedin a mountable housing and shaped plug 450. The conductor of choice,here shown as 424, is first fixated to the inside of a fastening maleelement, here shown as a precision machined screw without a taper 425,preferably made from material of similar properties, if not the samematerial, as the core material 364. The core material 364 is precisionbored and tapped to form the hollow geometry of a specified depth, hereas a cylinder with threaded walls, as its female mate. By fastening thetwo together as shown, the surface, layer, or thickness, is defined fromthe end of the conductor 424 to the exterior of the device in thedirection of the breach. If needed, the fastening elements can befurther fixated and/or seams hermetically sealed with adhesives,welding, or some other means.

FIGS. 5A-5D show another configuration of the elongate element where thedetection portion of the second conductor is spread out in an expandedpattern to, cover a wider area and increase the sensitivity. Thesurface, layer, and thickness and volume here are shown constructed of ahomogeneous material. FIGS. 5A and 5B are the sectional views and FIGS.5C and 5D are the top views of the conductor. In FIG. 5C, the conductorhas been spread out in a star shaped pattern but it will be appreciatedthat there is a myriad of possible patterns. Such an arrangementpresents an electrically conductive line or curve over a wide, shallowarea to detect the developing breach and particularly suitable forsurfaces subject to abrasive types of wear. The spread out distalportion may reside at the same depth from the direction of theanticipated breach in FIG. 5A or, as in FIG. 5B, have optionalprotuberances 522 and depressions 523 at certain points along its lengththereby presenting an array of points at a shallower level. In either ofthese configurations, the conductor 521 is equidistant at two or morepoints along its length closest to the surface, layer, or thicknesssubject to breach. As seen in FIG. 5D, the expanded pattern constitutesan electrically conductive dotted line or curve, where the dots are theprotuberances, in contrast to the smooth line and curve in FIG. 5C.

FIGS. 6A-6D show yet another configuration of the second conductor wheretwo or more elongate elements are assembled and coupled in amultipronged formation pointing toward the direction of the breach. InFIG. 6A, Conductors 621 and 622 have branches ending at layer 363 and361, respectively. The prongs of the two conductors are arranged in astaggered array, as shown in a top view FIG. 6B, thus enabling detectioncoverage over a wider area of a partial and a full thickness breach. Aconfiguration where the branches of two conductors 621 and 622 arecrisscrossed is shown in cross sectional views in FIG. 6C and, rotated90 degrees, in FIG. 6D. If desired, the staggered arrangement can beproduced with branches of different lengths. The prongs may be uniformin shape or a combination of different shapes as depicted in the earlierfigures above.

FIGS. 7A-7B depict location and orientation of the elongate elements ofthe second conductor in a cross sectional view with the principlesdescribed above in a structure with a convex surface, layer, orthickness. In a structure having a hollow volume 780, such as anenclosure or luminal structure, the detection portion of the conductors424 shown in loops terminate distally at different depths below thesurface, layer, or thickness to be monitored. With conductors 425 and426, the spiral ends transect tangential planes 771 at the fullthickness of the surface and 772 at an even deeper layer in the core ofthe structure, respectively. Regardless of the angle of approach, it isreadily seen that the longitudinal axis of the elongate elementtransects a plane of the convex surface, layer, or thickness subject tobreach. Shown with the volume comprising a solid cored structure 790,the conductors 222 are placed with their longitudinal axes radiatingfrom the core toward the surface, layer, or thickness to be monitored760 ending at partial thickness 761 and full thickness 763. Instructures that are heterogeneous, shown here as biphasic with material764 concentrically wrapped around a core material 766, it may beadvantageous to have the core material form optional projections orprotuberances here shown as cones 764 and 765 around the conductors. Thealternating peaks and valleys of the two materials dovetail to providemechanical stability to prevent delamination and/or hinder shearingforces at the interface that could tear the conductor and compromise itsintegrity.

FIGS. 8 and 9 depict location and orientation of the elongate elementsof the second conductor in a cross sectional view with the principlesdescribed above in a structure with a concave surface, layer, orthickness. The base of the structure 850 is partial and curved in dottedlines for a fastening mechanism to immobilize the component, such as adevice housing, to the body. An optional configuration where it isnarrowed and/or extended to form a neck 852 for the connection is shownin dashed lines. Alternatively, the concave structure, such as a luminalenclosure or connector component, is fastened to another part of thedevice. The detection portions of the conductors 821 and 822 radiatedistally toward the core of the concavity and terminate in differentlayers of the structure. They may be combined either singly or groupedin a staggered array (not shown). Conductor 823 has a multiprongedformation of elongate elements aimed toward the concavity in thedirection of the breach. The conductors typically extend proximallythrough the structure and drape along the back to reach and connect tothe logic circuit, which can be placed in a variety of locations. InFIG. 9, the base of the concave surface, layer, or thickness is wide andextend to cover its entirety in an optional configuration. Conductors424 are shown with a spiral configuration with termination distally atvarious depths. Tangential planes 971 at the full thickness of thesurface and 972 at an even deeper layer are transected by theirrespective conductors, 921 and 922. Regardless of the angle of approach,it is readily seen that the longitudinal axis of the elongate elementtransects a plane of the concave surface, layer, or thickness subject tobreach.

Referring now to FIGS. 10A-10C show where the elongate element 1021 isin the continuous loop configuration of a long spiral, coil, or helixwith radial axes 1031 oriented toward the direction a surface, layer, orthickness subject to breach. In this configuration, the conductor seenfrom the top (not shown) presents at the desired depth an electricallyconductive discontinuous line or curve of dots and/or dashes formed bythe peaks 1022 to detect the breach. In a longitudinal sectional view(FIG. 10B) and a cross sectional view (FIG. 10C), this configurationwill enable detection over a cylindrical surface with a singleconductor. This configuration (FIG. 10C) also enables detection of aninternal breach, for example a breach of a concave surface or layer of ahousing or luminal structure, initiated in the internal core volume thatpropagates laterally toward the surface with the radial axis 1032directed inward.

In FIGS. 11A-11D, how this loop or coil configuration of the elongateelement can be applied to surfaces, layers, or thicknesses with morecomplex contours or silhouettes is shown. In the sectional view FIG.11A, the detection portion 1021 of the coil presents an electricallyconductive spiral to detect a breach in a protuberant or thickened edgecommonly used to reinforce and increase durability of an edge, forexample, a leaflet of a cardiovascular valve. The radial axis 1131 ofthe elongate element is shown intersecting the tangential plane 1132 ofthe surface, layer, or thickness. Surfaces having a mixture of flats,protuberances, and indentations like many naturally occurring in thebody, such as joint articular surfaces, are shown from a simplifiedcross sectional view in FIG. 11B, projectional view in FIG. 11C, and atop view in FIG. 11D. Using the mold for the part, the conductor 1122can be formed, bent, and wound into shapes that faithfully follow thecontour so that it is equidistant at two or more points 1121 along itslength closest to the surface, layer, or thickness subject to breach.The shallower portions of the conductor, here shown in a continuous linein FIGS. 11B, 11C, and 11D, form conductive curves projecting to thedirection of the breach and are oriented to the contour of the surface,layer, or thickness. In all these configurations, the connection to thecircuitry is in a deep, protected part of the device and oriented awayfrom the area prone to the breach.

FIGS. 12A-12C, 13A, 13B, 14A-14C, 15A, 15B, 16A, 16B, 17A, 17B, 18A-18D,and 19, illustrate how the breach detection system is deployed invarious exemplar applications in orthopedic prosthesis, the hip, asimple ball and socket joint, and the knee, a highly complex joint,encompassing most, if not all, of the types of motions and forces ajoint experiences while static or in motion. It will be appreciated thatthe applications are not limited to these two joints and can besimilarly applicable to unicompartmental knee joints and other joints orpartial joints in the body. It will further be appreciated thatconfigurations of the elongate elements described in the other figuresabove, while not shown here, can be deployed in the fashion described tosuit the situation. The teachings will be applicable to naturallyoccurring, synthetic, biologically derived, or hybrid materials used insuch devices including but not limited to metal alloys, polymers,ceramics, and biologics, and in articulating contacts whethermetal-to-metal, metal-to-polymer, metal-to-ceramic, polymer-to-ceramic,polymer-to-polymer, ceramic-to-ceramic, and to their biologicequivalents and hybrids.

FIGS. 12A-12C, 13A, 13B, 14A-14C, 15A and 15B show deployment in thetotal knee replacement joint comprising two components, the femoral 1230and the tibial 1240. The patellar component is not shown here as it isnot load bearing but the teachings can similarly apply. The tibialcomponent itself typically comprises two parts, an articulating plate orinsert 1250 above and a support plate 1260 below as shown in FIGS. 12Aand 12B. The femoral component sits on the contoured superior surface ofthe tibial articulating plate as shown in FIGS. 13A and 13B. FIGS.14A-14C depict the variety of wear and tear forces that the jointexperiences during different stances and movements. In FIGS. 15A and15B, the operation of the system is depicted. The tibial articulatingplate is described in these teachings as made of polymer, such as ultrahigh density polyethylene, but can be made of any biocompatiblematerial. While the system is not shown embedded in the tibial supportplate, the teachings can be similarly applied. The tibial support plateis typically made of alloy and separated from the hostile conditions bythe articular plate, which bears the brunt of the wear and tear. Thus,no meaningful wear and tear to this part is anticipated unless thedamage to the articulating insert extends far beyond what is detectable.Note that the teachings will be applicable to partial deployment orreplacement of only a part, a component, a single articulation, or acombination thereof.

Referring now to FIG. 12A, the tibial component is anchored and fixatedinferiorly with a post 1273 to the surgically truncated tibia. Thecircuit and antenna 151 and a first conductor 110 on a shieldedsubstrate are fixated away from articulating and radiofrequencydisadvantaged areas, here placed in an exterior facing area on theanterior surface, of the polymer articulating plate. The polymer plate1250 with the circuitry 151 fit on top of the adjoining area in thealloy plate 1282. Optionally, the anterior surfaces of the platesadjacent to the substrate can be undercut, as shown here, in order toform a smooth contour over the anterior surface of the tibial component.The plane of the antenna is relatively in parallel to the surface of theoverlying tissues and skin on the anterior part of the knee. In thislocation, the incoming radiofrequency signals are relatively free frominterference by the metallic components, which are behind the antennaand shielding. FIG. 12B shows the superior articular surface of thepolymer plate, the concave area of articulation in contact with thefemoral component 1255 in dotted lines, and two configurations of thesecond conductors 221 and 1122 embedded below. In FIG. 12C, the twoplates are disassembled like a clamshell. The inferior surface of thepolymer plate 1251 mates with the superior surface of the alloy plate1261, commonly with female 1252 and male 1262 mechanisms as anchors.While shown near the center of the component, one or more of thefastening mechanisms can be placed at any suitable location. Theseinterlocking mechanisms are preferably non-destructive on the alloyplate side in the removal of only the polymer plate to facilitate thereplacement of a worn polymer plate with a new one. Using this method ofreplacing only the worn part without replacement of the intact alloyplate would simplify the procedure and spare unnecessary bone loss. Twodifferent arrangements of the second conductors are deployed in exemplarfashion. Second conductors 221 isolated from each other run from thelogic circuit along the inferior surface of the polymer plate, penetratethrough at the desired points, and terminate at the desired depthsbehind the superior articulating surface. In this configuration, twodepths of breach can be detected. Second conductor 1122 runs from thelogic circuit along the inferior surface of the polymer plate,penetrates through at the desired point, and forms or connects to acontinuous coil of a complex shape with points along its lengthequidistant in depth from the articulation contact area on the superiorsurface. In this configuration, the coverage area for the breach of thesame depth over the articulation contact area, an uneven contour, isenlarged with a single conductor. Optional additional grooves 1271 orsunken areas can be undercut on the superior surface of the alloy plateto accommodate the section of the second conductor on the inferiorsurface of the polymer plate. Alternatively, the circuitry can bedesigned as a package or have its own interlocking mechanisms to fitsecurely onto either or both plates (not shown). The entire circuitrycould be further attached, encased, or hermetically sealed to thepolymer plate on its inferior, non-articular, surface in protectivematerial to form one fixed, solid piece, if desired. Alternatively, thepolymer insert may be constructed in two or more pieces, medial andlateral, each with its own conductors and circuitry (not shown). In thisconfiguration, each side can be monitored and, when impairment detected,replaced independent of each other.

The system incorporated in the femoral component 1230, which sits on thetibial component 1240, in anterior and side views, FIGS. 13A and 13B,respectively. The femoral component is fitted to the surgically shavedfemoral head and anchored with posts 1360. The logic circuit 130 andfirst conductor 110 is fixated away from articulating areas, here on theshielded interior side wall of the component. The antenna 140 on ashielded substrate is fixated away from articulating and radiofrequencydisadvantaged areas, here on the exterolateral side of the component andits plane relatively in parallel to the surface of the overlying tissuesand skin. In these locations, the incoming radiofrequency signals arerelatively free from interference by the metallic components, which arebeneath the antenna. In addition, the plane of the antenna is relativelyorthogonal to the radiofrequency vector thereby maximizing the captureof radiofrequency energy and strength of signal. Referring now to FIG.13B, a lead runs from the antenna, either penetrates the side wall at adesired point or cross over the edge, along the interior side wall toconnect electrically to the logic circuit. A second conductor 622 of thedouble prong configuration is shown. Each prong is embedded in thedesired depth and aimed toward the articulation contact area of thefemoral component 1380, runs away from the articulating surface subjectto breach, emerges out of the floor, joins the other prong, runs alongthe floor and interior side wall to connect electrically with the logiccircuit. In this configuration, two pinpoint areas, whether close orfar, subject to breach could be monitored simultaneously by oneconductor. Again, the entire circuitry could be further attached,encased, or hermetically sealed to the assembled femoral component inprotective material to form one solid piece, if needed.

In FIGS. 14A-14C, a selection of the various wear and tear forcesencountered by the knee are depicted with the articular planes of thecomponents transecting the load bearing axis. In a stationary position,a load or impact 1431 is directly delivered by the most distal portionsof the femoral component causing compression and dispersion forces 1432on articulating contact areas, esp. that of the polymer plate. A changein stance would shift the load and center of such forces to other areaswhile its axis is still transected by the articular planes. Rotation,abduction and adduction, would cause corresponding shearing forces andload shifts in the same direction 1434. Flexion and extension causes amixture of rotational and frictional forces 1433.

FIGS. 15A-15B shows the progression of the accrued wear and tearresulting in pitting and cracking in the softer polymer plate therebyexposing the embedded second conductor in the breach. Interstitial fluidenters the breach and the ions electrically bridge the second conductorwith the exposed first conductor enabling the logic circuit to send abreach signal. During examination of the device, a radiofrequency reader1550 is held over the hermetically sealed capsule containing the circuitand antenna and an interrogation signal is sent 1570 and a signal 1580indicating “breach” or “no breach” is returned and shown on the displaypanel 1560. Depending on the configurations of the embedded secondconductors, partial breach, breach location, and the extent of thebreach could be detected and displayed. If the wear and tear can bedetected early, prior to any degradation of the underlying alloy plateor the femoral component, the impaired polymer plate can then bereplaced in a relatively minor procedure without replacing the tibiallyfixated alloy plate, thereby sparing the bone tissue.

In FIGS. 16A-16B, a selection of the various wear and tear forcesencountered by the hip are depicted and the system is shown deployed inthe total hip replacement joint comprising two components, theacetabular 1651 and the femoral 1652. In a stationary position, a loador impact 1631 is directly delivered by the femoral head causingcompression and dispersion forces (not shown) on articulating contactareas, esp. that of the polymer liner. A change in stance would shiftthe load and pressure point of such forces to other areas in the liner.Rotation, abduction, adduction, flexion, and extension 1633 would causecorresponding shearing and frictional forces in the same direction.Normal movement of the leg is a mixture of these actions and wouldresult in a combination of these forces in various degrees affectingboth the acetabular liner and the femoral component. The logic circuitsand their respective antennas 152 and the first conductors 110 are shownoriented toward the outside of the body, typically in an antero-medialor postero-lateral direction with the planes of the antenna fixatedrelatively in parallel to the surface of the overlying tissues and skin.The logic circuits, antennas, and first conductors are fastened to anexternal and radiofrequency advantaged area on the respective componentsor on the bone in which the respective components are anchored. In theselocations, the incoming radiofrequency signals are relatively free frominterference from the metallic components, which are behind the antenna.In addition, the plane of the antenna can be orthogonal to theradiofrequency vector in order to maximize transmission signal strengthand capture of radiofrequency energy.

The two disarticulated components and the disassembled femoral componentare shown in FIGS. 17A-17B. FIG. 17A shows how the spherical head fitsin the hemispherical cup of the acetabular component. As shown in FIG.17B, the femoral component typically comprises two parts, a sphericalalloy head 1654 with a cylindrical orifice 1740 into which the neck ofthe alloy femoral shaft 1751 is inserted. A double pronged secondconductor 621 is embedded with its tips at the predetermined depth inthe head projected outward. The prongs connect electrically in a lead1752, which emerges into the cylindrical orifice and runs along itsinterior wall and out of the head to connect to the logic circuit.Optionally, the circuitry could be further attached, encased, orhermetically sealed to the femoral head in protective material to formone fixed, solid piece, if needed. Grooves 1771 can be undercut eitheron the interior wall of the orifice or on the neck of the femoral shaftto fit the lead. The area for the logic circuit, antenna, and firstconductor 151 is undercut 1772 to fit the circuitry in order for thefemoral shaft to have a smooth, continuous contour. Alternatively, notshown here, the circuitry is attached to tissue that moves coterminouslywith the femoral head and shaft, so that it is not dislocated or torn bymovement of the body.

FIGS. 18A-18D depicts the deployment of the system in the acetabularcomponent. The alloy acetabular cup viewed from the side 1653 and front1653A are shown. A liner, commonly made of polymer, such as ultra highdensity polyethylene, but could be any kind of suitable material, viewedfrom the side 1655 and from the back 1655A are shown. A spiral secondconductor 423, embedded at a specified depth from and oriented towardthe concavity of the liner 1655, runs outward, emerges from the liner,runs along the convex posterior wall to connect with the logic circuitand antenna on a substrate 151. When the liner is fixated to theacetabular cup by anchors, the logic circuitry is draped over theexterior of the cup. As analogous to the knee prosthesis, theseinterlocking anchors are preferably non-destructive on the alloy linerside in the removal of only the polymer liner to facilitate thereplacement of a worn liner with a new one. The locations of thesefastening mechanisms can be placed at any suitable location so long asthe device can function properly. Using this method of replacing onlythe worn part without replacement of the intact alloy cup would simplifythe procedure and spare unnecessary bone loss. A slot on the edge of thecup 1822 and an area on the exterior of the cup 1823 can optionally beundercut such that the lead extension and circuitry could be inserted inplace and fastened. Alternatively, the circuitry could be fastened to awing on the acetabular cup (not shown) or the side of the pubic bone. Inthe case where the acetabular component is a singular piece, the secondconductor can be embedded in the same fashion as the liner, emerges fromthe liner in the back, runs along the convex posterior wall to connectwith the logic circuit and antenna 151. In this configuration, thecircuitry could be fastened to the exterior wall of or a wing on theacetabular cup or the side of the pubic bone. Optionally, the circuitrycould be further shielded, attached, encased, or hermetically sealed tothe acetabular liner and/or cup in protective material to form one solidpiece, if needed. While they are not shown here, it will be appreciatedthat the circuitry can be designed by one skilled in the art as apackage with fixating mechanisms in a myriad of ways to fit securelyonto the device.

FIG. 19 shows the system in operation, here with a hermeticallyencapsulated device with a ferrite core antenna. As in the knee, theprogression of the accrued wear and tear resulting in pitting andcracking in the softer acetabular liner exposes the embedded secondconductor in the breach to the surrounding interstitial fluid. Naturallyoccurring ions in the interstitial fluid enters the breach electricallyconnect the exposed conductor with the exposed first conductor enablingthe logic circuit to send a breach signal. During examination of thedevice, a radiofrequency reader 1950 is held over the antenna of theselected component and an interrogation signal is sent 1970 and a signal1980 indicating “breach” or “no breach” is returned and shown on thedisplay panel 1960. Each logic circuitry will have an identifying codeto indicate which component, if any, or both have been breached.Depending on the configurations of the embedded second conductors,partial breach, breach location, and the extent of the breach could bedetected and displayed. If the wear and tear can be detected early,prior to any degradation of the alloy acetabular cup or the femoralhead, only the impaired liner is then replaced in a relatively minorprocedure, thereby sparing the bone tissue.

While the present invention has been described herein with respect tothe exemplary embodiments and the best mode for practicing theinvention, it will be apparent to one of ordinary skill in the art thatmany modifications, improvements and subcombinations of the variousembodiments, adaptations and variations can be made to the inventionwithout departing from the spirit and scope thereof.

What is claimed is:
 1. An implantable device in the body comprising: a solid structure covering a volume with a surface, layer, or thickness subject to wear; a first electrical conductor located internally or externally of the said covering structure; an electrically conductive array including one or more elongate conductive elements embedded behind said surface, layer, or thickness of the said covering structure and isolated from said first electrical conductor, wherein said conductive elongate elements project in a direction from an interior toward a region subject to wear; and a wireless signaling circuitry coupled to the first electrical conductor and the electrically conductive array; wherein an electrically conductive fluid electrically bridges the first electrical conductor and the electrically conductive array to enable the circuitry to emit a detectable wireless signal warning when the wear of the surface, layer, or thickness exposes at least one distal portion of one or more of the conductive elongate elements. 